In twin screw compressors, the bores for the two rotors overlap such that the bores make a single cavity having the outline of a figure eight with cusps located at the waist portion of the figure eight. Conventionally, one of the cusps is made up of a slide valve and a slide stop. The slide stop changes the volume ratio of the device in accordance with its position while the position of the slide valve controls the capacity of the device. U.S. Pat. No. 4,678,406 is exemplary of the prior art devices employing a slide valve and slide stop.